The present invention relates to an actuator comprising an output member, a resilient element connected to said output member so as to urge it in a first direction, and a hydraulic rotation damper.
Such damped actuators are well-known in the art. In particular, such actuators are used in closing mechanisms for hinged members, such as doors, gates or windows, to effect automatic closure of the hinged closure member without slamming. Such hydraulic components are however delicate and usually badly suited for outdoors use. They are more particularly quite sensitive to temperature variations and are also often subject to leakage problems.
Examples of such actuators were disclosed, for example in U.S. Pat. No. 4,825,503 and UK Patent Application GB 2 252 790. These actuators, using a rotation damper with a rotating piston, do however present several drawbacks. The rotation damper has an angular travel of less than 360° and is directly coupled to the actuator output, without any multiplication stages. Since in this application it is important for the damper to be as compact and unobtrusive as possible, the area of the piston is necessarily limited. To achieve the required damping torques, comparatively high hydraulic pressures will thus be required. This makes it more difficult to prevent leaking, in particular through the damping adjustment valve, which is in fluid connection with the high-pressure side of the damper.
A further drawback is that it is difficult to achieve a good contact between the rotating piston and the inner wall of the cylinder. In fact, the rotating piston is formed by a rotating vane which has a free edge engaging the inner wall of the cylinder. Manufacturing such a vane and rotatably mounting it into the cylinder so that it fits exactly against the inner side of the cylinder, is a quite complex operation. Consequently, the production of the damper is relatively expensive and since the rotating piston will usually not fit exactly against the inner wall of the cylinder the hydraulic fluid has to be sufficiently viscous to be able to produce the required high pressure. A drawback of such viscous fluids is that their viscosity is usually quite strongly dependent on the temperature so that the known dampers are not appropriate for outdoor applications.
As an alternative, a different type of actuator has been disclosed in U.S. Pat. No. 4,097,957. This actuator is arranged for automatically closing a sliding type door. It comprises a fixed damper shaft and a cylinder barrel rotating together with the piston around the damper shaft. The rotation of the piston is converted into a translational motion thereof over a nut-and-screw transmission between the piston and the damper shaft. Rotation of the piston and cylinder barrel is achieved by means of a belt wound around the outside of the cylinder barrel. The travel of this rotation damper is thus not limited to an angle smaller than 360°. On the contrary, the cylinder barrel rotates several times around the damper shaft when the sliding door is opened or closed as a result of the relatively small outer diameter of the cylinder barrel. The closing force is obtained by a spiral spring which is arranged between the rotating cylinder barrel and the fixed damper shaft and which is wound up when opening the sliding door.
A drawback of the actuator disclosed in U.S. Pat. No. 4,097,957 is that for a given size of the spiral spring, which is limited by the dimensions of the actuator, the closing force (torque) which is exerted by the spring to effect closure of the closure member is limited due to the fact that it has to be able to be wound up and unwound over a number of rotations. In other words, the spring has to be a relatively weak spring so that it cannot assure a reliable closing of the closure member (sliding type door).
A damper which comprises a rotating damper shaft which is screwed into a piston so that the rotation of the damper shaft is converted into a translational movement of the piston within the cylinder barrel is disclosed in AT 393 004. This damper is however not an actuator since it doesn't comprise a resilient element. Moreover, an important disadvantage of this damper is that, in order to achieve a sufficiently large displacement of the piston in the cylinder, the threads on the damper shaft must have a very large pitch, namely a pitch which is so large that only a rotation of about 180° of the damper shaft is needed to displace the piston from its uppermost to its lowermost position in the cylinder. Such a large step causes high frictional forces which hamper the opening or closing of the closure member, especially when the hydraulic fluid within the damper is under a high pressure.